It is frequently necessary, for instance in a manufacturing operation, to scan the surface of a rapidly moving workpiece, for instance a web being processed, in order to read indicia or codes therefrom or to ascertain if the surface has a desired pattern, uniformity, or other visible characteristic. In stocking operations the reader can read bar codes which are invariably perpendicular to the direction of movement of the items being scanned.
Since the object is moving, it is necessary to somehow freeze the image on its surface. This can be done most simply strobe-fashion by exposing the surface for a very short time to a powerful light source so that a fixed camera or objective system can take a very short image-freezing exposure. Such a procedure is normally not considered convenient or practical.
Accordingly recourse is had to moving either the camera, the objective system, or a mirror arrangement synchronously with the workpiece in order to get a long enough exposure for effective imaging. Such arrangements have the considerable disadvantage that the equipment necessary for the movable camera or objective system is complicated and has a short time between failures in a normal production facility. In addition synchronizing the equipment with the movement of the workpiece is a complicated task, especially when workpiece speed changes. Such systems are therefore expensive, likely to fail, and are capable of losing synchronism and not being able to image sharply.